In a typical mobile telecommunication system, such as a Global System for Mobile communications (GSM), a mobile station operates in either a paging (idle) mode or an active mode. During the paging mode, a mobile station monitors a paging channel (PCH), located on the downlink of the control channel, used by a base station to alert mobile stations of incoming calls. A random access channel (RACH), located on the uplink of the control channel, can be used by the mobile station to transmit a request for a mobile originated call. When a connection (such as a phone call) is established, either incoming or outgoing, mobile terminated or mobile originated respectively, the base station assigns the mobile station to a traffic channel.
Pursuant to the Global System for Mobile Communications (GSM) the bandwidth is divided among many users by a combination of frequency division multiple access (FDMA) and time division multiple access (TDMA) channels. The FDMA part involves the division by frequency of 25 MHz bandwidth into 124 carrier frequencies spaced 200 Khz apart. Each of these carrier frequencies is then divided in time, using a TDMA scheme. At least one of the carrier frequencies, known as the common control channel, is used to carry various control channels. The remaining carrier frequencies (traffic channels) are used for user data and voice communications. In a TDMA scheme, a number of different mobile stations can use the same carrier frequency, but at different times. Each carrier frequencies include a repeating frame structure, wherein the frame contains time slots 0 through m-1. Each time slot can be allocated as a receive channel or a transmit channel for a different mobile station.
Referring now to FIG. 1, there is illustrated a block diagram of a physical common control channel. The physical common control channel is made up of a repeating multi-frame 100 of 51 frames 116. The multi-frame 1800 includes a Frequency Correction Channel (FCCH), frames 116(0), 116(10), 116(20), 116(30), 116(40), followed by a Synchronization Channel (SCH), frames 116(1), 116(11), 116(21), 116(31), and 116(41), a Broadcast Control Channel (BCCH), frames 116(2 . . . 5), and an Idle Frame, frame 116(50). The remaining 36 frames include logical channel types such as caging channels (PCH), frames 116(6 . . . 9, 12 . . . 19), access grant channels (AGCH), 116(22 . . . 29, 32 . . . 39, 42 . . . 49), Common Control Channel (CCCH), Stand-alone Dedicated Control Channel (SDCCH) and Slow Associated Control Channel (SACCH).
The paging channels (PCH) are divided into paging channel groups of four frames, frames 116(6 . . . 9), frames 116(12 . . . 15), and frames 116(16 . . . 19), wherein each particular frame group forms a particular logical paging channel. The mobile station served by the base station are divided into groups, wherein each group is associated with a particular logical paging channel. While in the paging mode, the mobile stations monitors only the particular logical paging channel associated therewith. Likewise, the base station only pages the mobile station using the associated logical paging channel.
The base station uses the paging channel monitored by the mobile station to notify the mobile station of incoming calls. When the subscriber at a mobile station wishes to place an outgoing phone call, call origination, the mobile station transmits a request to place an outgoing call using one of the random access channels (RACH). Upon reception of the RACH the base station uses one of the access grant channels 116(22 . . . 29, 32 . . . 39, 42 . . . 49) to assign a receive and transmit channel to the mobile station.
Referring now to FIG. 2A, there is illustrated a block diagram of the traffic channel (TCH), referenced generally by the numeric designation 200, pursuant to the GSM specifications. The traffic channels 200 are used to carry speech and data traffic. The traffic channels 200 use a repeating TCH multiframe 205 which includes 26 frames 116. The length of the TCH multiframe is 120 ms, and thus each frame is 4.615 ms in length. Out of the 26 frames 116, 24 are used for traffic 116a, one frame is used for the Slow Associated Control Channel (SACCH) 116b, and one frame is unused, the IDLE frame 116c. Each of the 24 frames used for traffic include eight 0.576 ms burst periods, known as slots 210. Each of the slots 210 can be allocated to a different mobile station. Depending on whether the traffic channel 200 is a downlink channel or an uplink channel, the mobile station either receives or transmits data in bursts during the allocated slot 210. Wherein the traffic channel 200 is an uplink channel, the mobile station transmits data in bursts, while if the traffic channel 200 is a downlink channel, the mobile station receives data in bursts.
Each slot 210 of frames 116a allows for transmission of 156.25 bits of data, which include two 57-bit data blocks 215, 26 midamble bits 220, 2 stealing bits 225, 2 sets of 3-bit tail bits 230, and 8.25 guard bits 235. The two 57-bit data blocks 215 are used to carry user data or voice communications while the remaining bits are for control and synchronization purposes. As noted above, each slot is 0.576 ms in duration, thereby corresponding to a bit transmission rate of 270.833 Kbps on the traffic channel 200.
Referring now to FIG. 2B, there is illustrated an active mode timing diagram for a mobile station. A mobile station engaged in a phone conversation, i.e., in the active mode, is allocated one slot 210a of a downlink traffic channel 200 for receiving data bursts, and one slot 210b of an uplink traffic channel 200 for transmitting data bursts. The downlink traffic channel and slot 210a position wherein the mobile station receives the data burst is known as the receive channel, while the uplink traffic channel 200 and slot 210b position wherein the mobile station transmits the data burst define a transmit channel. Pursuant to GSM specifications, the receive channel and transmit channel are staggered, such that the traffic channel follows three slots behind the receive channel.
Additionally, mobile stations routinely measure the received signal strength of the signal received from the base station serving the mobile station as well as surrounding base stations. The foregoing permits conducting a continuous phone conversation while the mobile station traverses the coverage area of one base station and enters the coverage area of another base station. The time period wherein the mobile station measures the receive signal strength is known as a monitor cycle 240. Monitor cycles can occur anywhere within the frame but typically occur during the TDMA frame between the transmit channel and the receive channel. To satisfy some GPRS scenarios the monitor cycle must occur between the receive and the transmit.
In recent years, the use of mobile stations has increased exponentially. Whereas ordinary wireline phones require connection of the terminal to a wireline, mobile station users can engage in telephone conversations anywhere within a vast service area of the cellular telecommunications network. In addition to voice communication services, wireline telephones are often used for access to data services and the internet. Although recent advances in broadband technology allow for cable connections, digital subscriber loops (DSL), local area network (LAN) connections, and Ethernet connections, each of the foregoing have the common drawback of requiring a wireline connection. Therefore, another major benefit mobile stations provide is wireless access to the internet and data services.
However, many mobile telecommunications systems are based on circuit switched radio transmission. At the air interface, complete transmit 210b and receive channels 210a are allocated for a single user for the entire call period. Data on the internet, and many data services, is transmitted in packets. For example, the Internet Protocol (IP) is used to packetize data transmitted on the internet. Allocation of a complete traffic channel 200 for a single user for an entire internet or data service session results in highly inefficient resource allocation. Alternatively, a packet switched bearer scheme, wherein a channel is only allocated when needed and released immediately after the transmission of the packets, results in a better utilization of the traffic channels 200.
General Packet Radio Service (GPRS) is a cellular packet data technology developed for GSM which applies a packet radio principles to transfer user data packets in an efficient way between mobile stations and packet data networks, such as the Internet. GPRS provides fast connection session establishment times, and billing based on the amount of transferred data.
In conventional GSM, a receive time slot 210a and transmit time slot 210b are allocated to a mobile station for the duration of a phone call, regardless of whether data or voice are transmitted. In contrast to GSM, receive and transmit time slots 210 are allocated separately and only when data packets are sent or received. During the periods of data packet transmission/reception, GPRS allows for allocation of multiple time slots 210 to a single mobile station. After transmission or reception, the allocated time slots 210 are released. In this manner, multiple users can share a traffic channel 200.
A GSM telecommunication system supports GPRS by allocating traffic channels 200 for GPRS packet traffic. A traffic channel 200 allocated for GPRS traffic is known as a packet data channel (PDCH) The PDCHs can be allocated dynamically depending on the current traffic load for voice and data communications in the mobile telecommunication system. Additionally, GPRS also includes a number of logical channels, such as the packet broadcast control channel (PBCCH), the packet common control channel (PCCCH), and packet dedicated control channels. The foregoing burst transmission and reception periods for voice, as well as packet data reception and transmission are achieved by selectively enabling and disabling the receiver and transmitter components of the mobile station. Mobile stations typically contain microprocessors and digital signal processing (DSP) cores. The microprocessor is responsible for controlling the receiver and transmitter components of the mobile station and running a protocol stack, while the DSP core is responsible for baseband processing the received signal and transmitted signal. The receiver and transmitter components require timing critical operation for precise synchronization with the TDMA scheme.
The timing critical operation of the receiver and transmitter are tedious tasks for the microprocessor which is more suitable for more general purpose tasks. Additionally, the microprocessor consumes considerable power from the battery in the foregoing tasks, thereby reducing the battery life of the phone. To alleviate the computational load and as well reduce the power consumption, the timing critical operations are off-loaded to time critical hardware.
The time critical hardware can include comparators, and counters, as well as internal clocks. Although the foregoing achieves some power savings, considerable die space is consumed. Furthermore, as enhancements are added to GSM, such as GPRS, additional hardware increases on an exponential basis. Therefore, addition of hardware is a non-scalable solution. While it is extremely important to reduce power consumption it is also important to have a coprocessor architecture that is as small as possible since die size is an important factor also.
Accordingly, it would be advantageous if the power consumption could be reduced.
It would also be advantageous if a scalable architecture could be developed to adapt to modifications and enhancements of mobile telecommunications systems.